The invention is directed to an arrangement for dry grinding preparation of grain type foodstuffs and feedstuffs, such as grain, particularly for cleaning, separating into different fractions and preferably for sorting out foreign matter such as sand, stones, and other inclusions, which comprises a size grading unit, e.g. screens, as well as a gravity grading unit, e.g. as a stone sorter, light grain sorter, etc.
The quantity of specialized machines in a milling installation, also known as a mill, for dry grinding preparation of grains, also known as cleaning, has decreased sharply in recent years. On the other hand, a group of standard units, such as screening devices and stone sorters, as well as light grain sorters to an increasing extent, are to be found in almost every new milling installation. Every unit or apparatus, respectively, is conceived with consideration to its specific task and is provided with suction air, vibrators, etc. The very specific design makes it possible to use the required air, as well as the oscillating energy, in a determined manner and at the lowest possible costs for construction and operation, so that an increased throughput capacity and a higher work quality can be achieved at the lowest possible installation costs in comparison with previous practice.
The majority of milling installations being constructed at present comprise four adjacent building sections, a first for the silo, a second for the grinding preparation, a third for the grinding or milling, and a fourth for the finished products.
The machines for grinding preparation, as well as those for grinding, are distributed on four or five floors. According to desired storage capacities, the storage silos usually rise above the mill buildings. A natural feature of storage silos, namely the discharge through openings in the floor with a corresponding downward movement of the product as a result of gravitational force, has likewise been made use of for many decades in machines for dry grinding preparation. In this case, also, the product is fed into the machines on the uppermost floor so as to move downward floor by floor and from one machine to the other, respectively, only by means of the force of gravity, i.e. without the technical application of additional energy for transport.
Every milling specialist knows that the grinding preparation, particularly the dry grinding preparation (cleaning, separating, sorting, etc.) of the raw material must be accorded as much attention as the grinding itself. This is demonstrated in the fact that in most milling installations space is provided for the grinding preparation/cleaning machines to a sufficient extent that no immediate need for a further concentration of same is known.
A fundamental disadvantage in dry grinding preparation results from the floorwise connection of the grinding preparation machines That is, for the sorting, grading and separating process, the entire product or material flow is fed to the respective machine in a planar thin layer or a thin falling veil. The product flow is bunched together again for transfer to the next machine and then spread out once again in a planar manner after the transfer.
A specially designed inlet portion is used for the uniform planar formation of a product bed. This is to prevent the initial part of the machine from being poorly utilized for the work demanded of it with respect to surface area.
The idea of arranging one machine next to the other in a row on the same floor has often been toyed with. From the point of view of working quality, this would be an advantage. However, since every machine requires different optimum conditions, this would require transition pieces which would be costly in terms of design, particularly when the adjacent machines oscillate in the direction of one another. It has been shown repeatedly in process technology that machines with large surface-area dimensioning are difficult to control. Disturbances are detected at a late stage, so that a small disturbance in one stage can often have disadvantageous consequences for the subsequent stage over a longer period of time.